17 



were homogenized in an equal volume of distilled water using 

 a glass tissue grinder, and the homogenate was centrifuged 

 at 10,000 g for ca 20 minutes through a discontinuous gradient 

 consisting of layers of 25, 50, 75, and 100% Percoll. Over 

 97% of B. dimorpha NMB spores purified in this manner ex- 

 truded their polar filaments when ingested by ant larvae 

 (determined by phase microscopy of meconia) , indicating 

 that most immature spores had been removed. Slightly less 

 highly purified suspensions suitable for use in routine 

 propagation of the parasite were obtained by centrifuging 

 the crude homogenate at 750 g for 20 minutes in a 50% solution 

 of Percoll. After all centrifugations with Percoll, the 

 spores were washed three times with distilled water, and 

 the volume was adjusted to ca 10 spores/ml. Spore suspen- 

 sions were stored at 4° C. 



